Embodiments of the invention relate generally to fin-shaped field effect transistors (FinFETs) formed on a bulk silicon (Si) substrate as opposed to a silicon-on-insulator (SOI) structure. More specifically, embodiments of the invention include a method of forming a bulk silicon FinFET and a resulting integrated circuit structure.
In integrated circuit (IC) structures, a transistor is a critical component for implementing digital circuitry designs. Generally, a transistor includes three electrical terminals: a source, a drain, and a gate. By applying different voltages to the gate terminal, the flow of electric current from the source to the drain can be turned on and off. A common type of transistor is a metal oxide field effect transistor (MOSFET). One type of MOSFET structure is a “FinFET,” typically formed upon a semiconductor-on-insulator (SOI) layer and buried insulator layer. A FinFET can include a semiconductor structure etched into a “fin” shaped body, with one side of the fin acting as a source terminal and the other side of the fin acting as a drain terminal. A gate structure, typically composed of polysilicon and/or a metal, can be formed around one or more of the semiconductor fins. By applying a voltage to the gate structure, an electrically conductive channel can be created between the source and drain terminals of each fin in contact with the gate.
In some cases, a FinFET may be desirable in IC structures which do not include an SOI layer with a corresponding buried insulator layer. For example, manufacturing dynamic random access memory (DRAM) can include forming transistor structures on a bulk substrate instead of an SOI-type structure. Planar devices can be formed conventionally within the bulk substrate without substantial modifications. A FinFET transistor may also be adapted for use on bulk substrate material instead of SOI. Conventional approaches to forming a FinFET structure on bulk substrate include forming a placeholder material on the bulk substrate, forming the rest of the FinFET structure, and replacing the placeholder material with a local insulator. The local insulator can act as a substitute for the buried insulator layer which is absent in the bulk substrate material.